Q. What are die casting's advantages over producing a design as a sand casting?
A. Compared with sand castings, die castings require little or no machining to meet specifications, can be made with thinner walls, can have all or nearly all holes cored to size, can be held within much closer dimensional limits, and are produced more rapidly in dies which can make many thousands of castings without replacement, rather than requiring new cores for each casting. Die castings have smoother surfaces and involve much less labor cost per casting. Sand castings, on the other hand, can be made from ferrous metals and from many nonferrous alloys not suitable for die casting which provide higher strength and wear resistance. Certain shapes not producible by die casting are available in sand castings, maximum size can be greater, tool cost is usually less and small quantities can be produced more economically but may require extensive machining.
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Q. What is the economic quantity level for conversion to a die casting from a sand casting, or other gravity casting process?
A. The key to determining the lowest economic production quantity level for a conversion from sand casting to die casting, or from many other lower volume production processes, depends largely on the configuration, size and complexity of the part. While the die casting process is most economic at higher volumes, die casting can achieve comparative savings at quantities at or below 2,000 pieces if extensive post-casting machining or surface finishing can be eliminated. CWM should be consulted so a proposed design, or existing part, can be evaluated early for die casting, and the design optimized for lowest-cost die cast production.
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Q. What are die casting's advantages over producing a design as an investment casting?
A. Investment casting is a high-precision process that employs alloys with properties similar to foundry alloys. Tooling cost is substantially lower than for die casting, but production costs are higher. Investment casting is competitive with die casting only at very low production volumes.
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Q. What are die casting's advantages over production by the thixomold(TM) process?
A. Thixomolding requires a thicker gate inlet which has a tendency to leave a rough surface finish at the gate location. The solid-liquid concentrations inherent in the process are variable, making predictability of part performance difficult. While thixomolders have stated dimensional accuracy comparable to the established tolerances of die casting production, their experience base has yet to be developed. Shorter tool life, compared to die casting, should be expected, since an all-liquid die casting shot has less abrasive characteristics than a semi-solid shot. Thixomolding cavity pressure is two times that of die cast pressure, with the potential for residual stresses mounting more quickly due to higher cavity distortion. With over twice the clamping load required for this process, cycle times are longer due to larger machine sizes, and additional time can mean higher costs. It is often difficult to accurately mold certain intricate net-shape features called for in a product design, which can be produced by advanced die casting technology.
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Q. When can die casting offer advantages over permanent mold castings?
A. Die castings can be made to closer dimensional limits and with thinner sections than permanent mold castings. Holes can be cored in die castings, and they are produced at higher rates with less manual labor. They have smoother surfaces and usually cost less per part. Permanent mold casting, however, involves somewhat lower tooling costs and can be made with sand cores yielding shapes not available in die casting.
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Q. What are die casting's advantages over producing a design as a plastic molding?
A. Compared with the most widely specified plastic injection moldings, die castings are stronger, stiffer, more stable dimensionally, more heat resistant, and are superior to plastics based on mechanical properties per unit of cost. Die castings have a high degree of permanence under load when compared to plastics and are far more resistant to ultra-violet irradiation, weathering and stress cracking in the presence of various reagents. Castings offer built-in EMI/RFI shielding, which is often a problematic and costly post-casting operation with plastic housings. However, plastic raw material costs less on a unit volume basis. It has color- inherent properties which tend to eliminate finishing. It is temperature sensitive and has a high degree of electrical resistance.
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Q. If you require a surface color on a component, and it is possible to produce the part as a plastic molding, won't the optimum choice be to produce the part as integrally colored plastic?
A. While plastic moldings offer the choice of resins in a range of integral colors, OEM designers and purchasers often choose post-molding decorative finishing for the fact that the desired color effect is not obtainable in an integral resin color, especially when color matching to other components is essential. Also post-molding finishing can often be performed at lower final cost, especially at lower volumes. In addition, the die casting process may be selected based on Al, Mg or Zn's rigidity, impact strength, heat resistance, dimensional stability, and built-in EMI/RFI shielding characteristics.
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Q. When can die casting offer advantages over producing a design as a stamping?
A. Stamping from sheet steel offers economy that is difficult to equal when a component can be made from one relatively simple stamping. Steel stamping dies that perform a single operation are less costly than die casting dies. The relative costs for tooling and processing depend on the number and types of dies and presses needed. When a highly complex stamping or several stampings are required, die casting can be a cost-effective alternative, and can achieve complex shapes impossible with a stamping. In the case of multiple stampings, costs of fixturing and welding added to the costs of fabricating the additional parts, can make die casting very competitive. Material costs for stamping may be substantially higher than indicated by published per pound costs due to high scrap rates. Stampings invariably consume more material than is contained in the end product, sometimes substantially more.
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Q. What are die casting's advantages over producing a design as a powdered metal part?
A. Die casting and powdered metal processes are highly competitive with respect to dimensional precision and part machining requirements. The advantage usually hinges on the orientation of features and desired wall thicknesses. The choice between die casting and powdered metal frequently depends on product size, weight or performance requirements rather than economics. Light-weight die castings can be made in sizes that exceed the capabilities of powdered metal. Powdered metal can be the choice when metals such as ferrous, stainless steel, and copper alloys are required to achieve strength, wear resistance, or high operating temperatures.
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Q. When can die casting offer advantages over screw machining?
A. Automatic screw machining entails the lowest tooling cost of any production method. Highly automated screw machines are not labor intensive. The process, which uses bar stock as raw material, offers very poor material utilization, however, sometimes less than 50%. The choice versus die casting will usually depend on production quantities, with the die casting advantage increasing as production rates increase. Unusually complex design shapes are routinely produced as die castings, while they would be costly or impossible as machined parts.
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Q. When can die casting offer advantages over producing a design as an extrusion?
A. Extrusions made from aluminum, magnesium, and zinc alloys exhibit strength and rigidity similar to die castings; however, the ductility is generally higher. Tooling and production costs are comparatively low, making the process very competitive. Extruded designs that require changes in cross section, or features such as holes and slots, can often be converted to die castings, eliminating the machining operations required for extrusions. The choice is usually governed by the number of machining operations, but occasionally by minor differences in material properties, such as strength or surface treatment characteristics.
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Q. When can die casting offer advantages over forgings?
A. Where a die casting alloy can satisfy the design requirements for strength and density, die casting will offer complex shapes not possible in forged parts, with thinner sections held to closer tolerances. A new generation of metal matrix composites, squeeze cast, and semisolid cast parts are offering significant cost savings over forgings at substantial weight reductions.
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